1. Field of the Invention
The present invention relates generally to an engine mount interposed between the power unit and the body of an vehicle, for a vibration-damping support of the power unit on the body, and more particularly to an engine mount of novel construction, having a stopper mechanism for cushionwise restriction of the level of displacement of the power unit relative to the body, as well as having spring characteristics that are easily tuned in consideration of the characteristics of the power unit and the body.
2. Description of the Related Art
To date, the practice has been to install a multitude of engine mounts interposed between the body and the power unit of a vehicle, to provide a vibration damping support of the power unit on the body. One known engine mount of this kind has a construction in which a first mounting metal member and a second mounting metal member disposed spaced apart from each other are elastically connected by a rubber elastic body. This kind of engine mount is installed with the first mounting metal member fastened to the power unit via a bracket fitting, and the second mounting metal member fastened to the body via a bracket fitting. With this arrangement, the power unit has a vibration damping support from below, through the agency of the engine mount.
As depicted in FIG. 11, with the engine mount installed in an vehicle, typically, for reasons pertaining to performance in terms of the support characteristics of the power unit 2 by the body 3, the principal axis of elasticity: a in the shear direction of the rubber elastic body 5 making up the engine mount 4 is positioned so as to incline diagonally downward to the inside, towards the center of the power unit 2. The term “inside” refers to the inside of the power unit 2, i.e. the torque roll axis side.
The direction in which the principal axis of elasticity is established in an engine mount has considerable effect on the vibration damping support characteristics of the power unit on the body. It is preferable to set and tune individually the principal axis of elasticity in an engine mount, depending on the particular vibration damping characteristics required for each marque and model of vehicle.
As one approach, JP-U-58-184048 proposes an engine mount of construction wherein the first mounting metal member and the second mounting metal member attached to the rubber elastic body are positioned at a relative incline, so that the direction of the principal axis of elasticity is inclined with respect to the direction of opposition of the first mounting metal member and the second mounting metal member. Another approach, proposed in JP-A-10-292850, is an engine mount of construction wherein, the second mounting metal member to be affixed to the body has a mounting bearing surface that projects out on an incline towards the body side.
Where the direction of the principal axis of elasticity in an engine mount has been established appropriately in this way, new problems are created. Namely, the relative incline angle of the first mounting metal member and the second mounting metal member varies, or the absolute angle of the first mounting metal member and the second mounting metal member varies. These problems make it difficult to set up a stopper mechanism in the bound direction.
Specifically, as taught in the above mentioned documents, in order to provide cushionwise restriction of excessive levels of displacement of the power unit relative to the body, it is important to provide a stopper mechanism in the bound direction in particular. This type of bound stopper mechanism is typically constructed by projecting the first mounting metal member and the second mounting metal member in the generally horizontal direction, situating them in opposition a predetermined distance apart, and forming cushion rubber on their mutually abutting opposing faces.
However, where as described previously the first mounting metal member and the second mounting metal member are inclined relative to one another, or where there is a large absolute incline angle of the first mounting metal member and the second mounting metal member, the two mounting metal members are substantially no longer positioned in opposition in the vertical direction. Thus, it became extremely difficult to form on the first mounting metal member and the second mounting metal member abutting faces of sufficient surface area, as generally flat opposed faces extending in the horizontal direction and positioned in opposition to each other in the bound direction (the vertical direction with the mounting installed).
Specifically, as taught in the aforementioned JP-U-58-184048, the abutting faces in the bound direction must be formed by inclined faces that spread out on an incline with respect to the horizontal. As taught in the aforementioned JP-A-10-292850, in order to form the abutting faces, a large abutting face that projects out appreciably to the outside of the first mounting metal member or second mounting metal member must be formed. Therefore these conventional stopper mechanisms may suffer from difficulty in producing effective load bearing performance in terms of stopper function in the bound direction, and a problem of enlargement in size and weight of the metal members, leading to a problem of adverse effect of the greater weight of the metal members against vibration damping characteristics produced by resonance.